1. Field of the Invention
This invention relates to molded applique products of the type made of synthetic resins having printing on a surface thereof and to a method of making the same. Products of this type are used, by way of example, to make automobile instrument panels.
2. Description of the Prior Art
Products of the indicated type have been made for many years by a method known in the art as an in-mold decorating process. This process, which has been in use since at least as early as 1972, was used to produce printed parts on polystyrene and polypropylene sheets that were, after printing, die cut and sent to injection molders to be in-molded into a finished product. By way of example, some of these products were plastic lunch boxes, pitchers, and canisters. In this process, the overlays or in-mold decoratives were produced by offset printing and/or screen printing, and the parts were flat and were held into the mold with a static charge. Because the overlays or in-mold decoratives did not contain complete (100 percent) ink coverage, it was possible to print on the rear surface of these parts and still have the molten plastic material fused to the rear surface of the plastic substrate, thus leaving a layer of plastic film on the outside to protect the graphics. In this process, the gating of the mold had to be such that the introduction of the plastic took place where there was no ink, since any ink present in this area would tend to move or distort. The bonding in this case would only take place between the clear plastic area of the overlay and the molding compound itself.
A molding method essentially the same as the in-mold decorating process described above is disclosed in U.S. Pat. No. 4,917,927. The patent claims novelty in the printing step wherein a synthetic resin sheet has an ink film applied to at least one side of the resin sheet wherein the ink film comprises one or more layers, each of which has a specific minimum thickness. The patent states that by this inking process that it is possible to produce a backlighting product. Backlighting products are well known in the art and are capable of making a pictorial image printed thereon look bright when viewed from the front if light is shown from the rear of the product. Products of this type are used to make automobile instrument panels. The patent discloses the printing on a flat resin sheet which is placed into a die into which a molten synthetic resin is injected pursuant to the in-mold technique discussed above.
The prior art techniques were not suitable for making a three-dimensional applique product of the type shown in the drawings. In fact, those skilled in the art believed it would not be possible to obtain the shape and configuration of this type while at the same time providing an acceptable decorative presentation. It was believed that during the in-mold process of the prior art the product would be deformed and thereby harm the decorative presentation. However, the development of monomer resins which can be polymerized in situ as an alternative to molten thermoplastic injection molding has overcome many of the problems associated with the injecting of molten plastic onto a printed substrate. One such development is the "METTON.RTM." liquid-molding resin. METTON.RTM. is a registered trademark of Hercules, Inc. (Hercules Plaza, Wilmington, Del. 19894-0001) for a proprietary blend of polydicyclopentadiene (PDCPD) formed by the metathesis polymerization of dicyclopentadiene (DCPD). The METTON.RTM. liquid molding resin involves the mixing of an "A" DCPD component with a "B" DCPD component within a mold cavity. The A and B DCPD components polymerize in situ to create polydicyclopentadiene at a reaction temperature of about 170.degree. C. to about 200.degree. C. METTON.RTM. resins have the advantage that less energy is required in the liquid molding of plastic parts than is needed for the thermoplastic injection molding thereof. Also, the polymerization reaction temperature of PDCPD is lower than the melt temperature of thermoplastic polymers whereby thinner substrates and inks, which are less temperature deformable, can be utilized in the production of back-lit products.